US3098089A - Stable lead alkyl compositions and a method for preparing the same - Google Patents

Description

United States Patent 3,098,089 STABLE LEAD ALKYL COMPOSITIDNS AND A METHOD FGR PREPARING THE SAME Shirl E. Cook and Wilford H. Thomas, Baton Rouge, La.,

assignors to Ethyl Corporation, New York N .Y., a corporation of Virginia No Drawing. Filed June 8, 1962, Ser. No. 200,930 6 Claims. (Cl. 260-437) 1 This invention relates to alkyllead compositions which are stable at temperatures above 100 C. It also relates to methods for inhibiting the thermal decomposition of alkyllead compounds when subjected to temperatures above 100 C., at which temperature thermal decomposition becomes appreciable.

Generally this invention contemplates inhibiting the thermal decomposition of alkyllead compounds in which at least one valence of the lead is satisfied by an alkyl radical.

More specifically, this invention is concerned with an improved process for separating alkyllead compounds from the reaction products accompanying their synthesis. It is also applicable to a method for inhibiting thermal decomposition of an alkyllead product during its purification and blending with other products in making commercial antiknock fluids. It is applicable to minimizing the possibility of thermal decomposition during storage or transportation of an alkyllead product. It is especially applicable to preventing thermal decomposition of undiluted alkyllead compounds where the likelihood of thermal decomposition is more of a problem.

As is well known, tetraalkyllead antiknock compounds generally are produced by reacting a sodium-lead alloy with.an alkyl halide. Due to recent marked improvements in the technology of alkyllead manufacture, thermal instability of alkyllead compounds during synthesis is no longer a problem. However, the tetraalkyllead compound so produced in admixture with various reaction by-products from which it must be separated. Separation is eifected by steam or vacuum distillation with subsequent purification of the tetraalkyllead distillate. Due to the toxic and unstable nature of tetraalkyllead antiknock compounds, these distillation and purification operations are subject to many difficulties.

In these distillation and purification operations meticulous temperature control and exact safety measures are of paramount importance. The rate of decomposition of the alkyllead compound increases rapidly with small rises in temperature above the temperature where thermal decomposition becomes appreciable. For example, decomposition of tetracthyllead occurs at the rate of approximately 2 percent per hour at a temperature of 100 C., which is the customary temperature used in separating tetracthyllead from the reaction products accompanying its synthesis. At temperatures above 100 C., the decomposition rate increases logarithmically so that a point is soon reached where external heat is no longer required and decomposition becomes selfpropagating.

Such likelihood of excessive decomposition is present also during blending, handling, storage, and transportation. Prior to diluting the alkyllead concentrate with scavengers, gasoline or other materials, the alkyllead compound remains a concentrate and the problem of excessive thermal decomposition exists, even though the temperature is maintained normally well below that of decomposition. For example, in the purification step wherein the tetracthyllead concentrate is washed and blown with air at atmospheric temperature to remove impurities, a sudden increase in temperature may occur due to the oxidation of triethylbismuth which is present as an impurity. Also pumps used in handling tetracthyl- 3,098,089 Patented July 16, 1963' lead occasionally freeze and the friction developed may cause a local overheating to a temperature above the temperature of decomposition of the tetracthyllead. Faulty Wiring, leaks onto steam pipes, and other accidental causes also may produce local overheating with resulting dangerous decomposition.

It is seen therefore that in those operations where an alkyllead compound is in the undiluted or concentrated state-viz, separation, purification, blending, transportation, and storagethe likelihood of excessive thermal de composition must be provided for and effectively combatted.

An object of this invention is to stabilize alkyllead compounds against thermal decomposition during one or more of the following operations: separation, purification, blending, transportation and storage.

The above and other objects of this invention are accomplished by incorporating with alkyllead compounds a relatively small quantity of a mixture of materials which has the property of synergistically inhibiting alkyllead thermal decomposition. The foregoing objects are also accomplished by conducting one or more of the foregoing operations in the presence of such a mixture of materials. The mixtures which have been found to possess these unexpected properties are referred to hereinafter as thermal stabilizers.

The synergistic thermal stabilizer mixtures of this invention are composed of two different chemical types of hydrocarbons which are used in conjunction with each other.

The first ingredient is a phenyl acetylenic hydrocarbon containing from 8 to about 12 carbon atoms in the molecule and preferably having the formula wherein R and R are hydrogen or alkyl groups. Phenyl acetylene, p-tolyl acetylene, cumenyl acetylene, p-tert-butylphenyl acetylene, 2,4-dimethylphenyl acetylene, and the like serve as examples. This first ingredienit is utilized in proportions of from about 5 to about 25 weight percent based on the weight of the alkyllead compound being stabilized. Departures from this proportion are permissible where the conditions of service and utility warrant or justify such departures.

The second ingredient utilized pursuant to this invention is a fused ring aromatic hydrocarbon containing from .10 to about 14 carbon atoms in the molecule. Naphthalene, l-methyl naphthalene, 2-methyl naphthalene, 1,4-dimethyl naphthalene, 1,8-dimethyl naphthalene, l-ethyl naphthalene, 2-ethyl naphthalene, '1-methyl-6- ethyl naphthalene, 1,2,4-trimethyl naphthalene, 1,4,5,8- tetramethyl naphthalene, and mixtures thereof serve as examples of this second ingredient. This ingredient is likewise utilized in proportions such that there is about 5 to about 25 weight percent thereof based on the weight of the alkyllead compound being stabilized. However, departures from such proportions are permissible where desirable or appropriate.

The foregoing combination of hydrocarbons when used in the amounts set forth above are very effective in substantially retarding or preventing thermal decomposition of the alkyllead compound at temperatures ranging from about C. up to about C. for extended periods of time. Moreover, the behavior of this combination of additives has been found to be synergistic, i.e., the thermal stabilization effectiveness of the whole is far greater than the sum total of its parts. This efiectiveness is achieved even when the above combination is diluted with other hydrocarbons, such as parafiins, cycloparaflins, and the The chief thermal decomposition products of alkyllead compounds are lead metal and hydrocarbon gas. Hence, a very good index of alkyllead thermal decomposition is liberation of this gas.

To illustrate the effectiveness of this invention, a series of direct comparisons were made of the decomposition characteristics of unstabilized and stabilized tetraethyllead samples. A thermostatically controlled hot oil bath was fitted with a stirrer, thermometer, and a holder for a small reaction tube. A 100 cc. gas buret beside the bath, and equipped with a water-containing levelling bottle, was connected by means of rubber tubing with the reaction tube after the desired sample was introduced into this tube. After the bath was brought to a Steadytemperature of 195 C., the sample-containing tube was quickly immersed in the bath and clamped with the leveling bottle adjusted to hold the gas buret in place at a zero reading. Then measured was the time during which the sample was held at 195 C. without pronounced thermal decomposition and consequent gas evolution occurring. Thus, the longer the time, the more thermally stable was the alkyllead composition.

With pure tetraethyllead used in 1 ml. amounts, pronounced thermal deterioration occurred almost immediately as evidenced by rapid gas evolution. In fact, the decomposition of unstabilized tetraethyllead will normally becomeuncontrollable if it is heated, whether rapidly or slowly, to even 130 C., unless it is possble to very rapidly cool it down to about 100 C. or below.

The remainder of the compositions tested in the manner described above and the results thereby obtained are shown in the following table.

TABLE Effect of Additives on Thermal Decomposition of Alkyllead Compounds at 195 C.

Numbers in parentheses following the ingredient designate the concentration thereof in terms of weight percentage based upon the weight of the tetraethyllead.

It will be noted that the compositions of this invention exhibited a high degree of synergistic effectiveness.

The above-described beneficial behavior of the thermal stabilizer mixtures of this invention also takes place with other alkyllead compounds such as triethyllead bromide and tetrapropyllead. In fact, these compounds when stabilized can be boiled and distilled at atmospheric pressure.

This invention is adapated to the stabilization of tetraethyllead and other alkyllead compounds at various stages after they have been formed and the diluents or excess .alkyl halide have been discharged from the autoclave. For example, one of the above thermal stabilizer combinations may be added in appropriate quantity to the alkyllead reaction concentrate just before the separation step which is conducted at a temperature close to the temperature where hazardous run-away decomposition is particularly prevalent. By adding one of the above thermal stabilizer combinations to the reaction concentrate just prior to distillation, the danger arising from unexpected temperature increases is substantially eliminated.

Most preferably the above thermal stabilizer combinations are employed to stabilize the alkyllead compound both in storage and in shipping and especially to stabilize any alkyllead concentrate, i.e., compositions containing at least percent by weight of alkyllead compound. If elevated temperature conditions are likely to be encountered, the addition of a small amount of thermal stabilizer mixture to the alkyllead compound will economically and satisfactorily eliminate most of the hazard involved. While meticulous temperature control and exacting safety measures have been successful in reducing to a minimum the hazards of processing and handling of tetraethyllead, the use of this invention provides a much greater factor of safety. Furthermore, the waste of the alkyllead product due to decomposition is considerably minimized through the use of this invention.

.This invention is useful in stabilizing alkyllead compounds in which at least one valence of the lead is satisfied by an alkyl radical. For example tetraethyllead, tetratrnethyllead, tetrapropyllead, dimethyldiethyllead triethylphenyllead, and triethyllead bromide can be successfully stabilized against thermal decomposition by incorporating therein a relatively small quantity of one of the thermal stabilizers of this invention. This invention is particularly well suited to the stabilization of any mixture involving two or more of the following compounds: tetrarnethyllead, ethyltrimethyllead, diethyldimethyllead, triethylmethyllead, and tetraethyllead.

What is claimed is:

-l. A method of inhibiting the decomposition of an alkyllead compound at temperatures of rfrom about C. to about C. which comprises incorporating with said compound from about 5 to about 25 weight percent based on the weight of the alkyllead compound of a phenyl 'acetylenic hydrocarbon having from 8 to about 12 carbon atoms in the molecule and having the formula CECE wherein R and R are selected from the group consisting of hydrogen and alkyl groups; and from about 5 to about 25 weight percent based on the weight of the alkyllead compound of a tused ring aromatic hydrocarbon containing from 10 to about 14 carbon atoms in the molecule.

2. In the process of producing an alkyllead compound by reacting a sodium lead :alloy with alkyl chloride and separating the thus produced alkyllead compound from the reaction mass by steam distillation, the step which comprises conducting said steam distillation in the presence of from about 5 to about 25 weight percent based on the weight of the alkyllead compound of a phenyl acetylenic hydrocarbon having from 8 to about 12 carbon atoms the molecule and having the formula CECE wherein R and R are selected from the group consisting of hydrogen and alkyl groups; and from about 5 to about 25 weight percent based on the weight of the alkyllead compound of a fused ring ring aromatic hydrocarbon containing from 10 to about 14 carbon atoms in the molecule.

3. A concentrated alkyllead compound with which has been blended from about 5 to about 25 weight percent based on the weight of the alkyllead compound of a phenyl acetylenic hydrocarbon having from 8 to about 12 carbon atoms in the molecule and having the formula CECH R2 wherein R and R are selected from the group consisting of hydrogen and alkyl groups; and from about 5 to about '5. The compisit-ion of claim 3 wherein said alkyllead 25 weight percent based on the weight 'of the alkyllead compound is tetr aethyllead.

compound of la fiused Ting aromatic hydrocarbon contain- 6. The composition of claim 3 wherein said alkyllead ing from 10 to about 14 carbon atoms in the molecule. compound is tetnaethyllead, said phenyl \acetylenic hydro- 4. The composition of claim 3 wherein said alkyllead 5 carbon is phenyl acetylene, and said fused ring aromatic compound is selected from the group consisting of tetrahydrocarbon is a methyl naphthalene.

methyl-lead, ethyltrimethyfllead, diethyldimethy-llead, triethylmethyllead, tetraethyllead, and mixtures thereof. 0 fefence s cited.

Claims (1)

1. A METHOD OF INHIBITING THE DECOMPOSITION OF AN ALKYLLEAD COMPOUND AT TEMPERATURES OF FROM ABOUT 100* C. TO ABOUT 195* C. WHICH COMPRISES INCORPORATING WITH SAID COMPOUND FROM ABOUT 5 TO ABOUT 25 WEIGHT PERCENT BASED ON THE WEIGHT OF THE ALKYLLEAD COMPOUND OF A PHENYL ACETYLENIC HYDROCARBON HAVING FROM 8 TO ABOUT 12 CARBON ATOMS IN THE MOLECULE AND HAVING THE FORMULA